Apparatus and method for transmitting reference signals in wireless communication system

ABSTRACT

The present disclosure relates to a pre-5 th -Generation (5G) or 5G communication system to be provided for supporting higher data rates Beyond 4 th -Generation (4G) communication system such as Long Term Evolution (LTE). The present invention relates to transmission of a reference signal in a wireless communication system, and an operation method of a terminal comprises the steps of: receiving control information for reference signals from a base station; and receiving the reference signals according to the control information. Further, the present invention also comprises embodiments different from the embodiment described above.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application claims priority under 35 U.S.C. § 365 toInternational Patent Application No. PCT/KR2016/004017 filed Apr. 18,2016, which claims priority to Korean Patent Application No.10-2015-0054654 filed Apr. 17, 2015, each of which are incorporatedherein by reference into the present disclosure as if fully set forthherein.

TECHNICAL FIELD

The present invention relates to transmission and reception of referencesignals in a wireless communication system.

BACKGROUND

To meet the demand for wireless data traffic having increased sincedeployment of 4^(th) generation (4G) communication systems, efforts havebeen made to develop an improved 5^(th) generation (5G) or pre-5Gcommunication system. Therefore, the 5G or pre-5G communication systemis also called a ‘Beyond 4G Network’ or a ‘Post Long Term Evolution(LTE) System’.

The 5G communication system is considered to be implemented in higherfrequency (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higherdata rates. To decrease propagation loss of the radio waves and increasethe transmission distance, the beamforming, massive multiple-inputmultiple-output (MIMO), Full Dimensional MIMO (FD-MIMO), array antenna,an analog beam forming, large scale antenna techniques are discussed in5G communication systems.

In addition, in 5G communication systems, development for system networkimprovement is under way based on advanced small cells, cloud RadioAccess Networks (RANs), ultra-dense networks, device-to-device (D2D)communication, wireless backhaul, moving network, cooperativecommunication, Coordinated Multi-Points (CoMP), reception-endinterference cancellation and the like.

In the 5G system, Hybrid frequency shift keying (FSK) and quadratureamplitude modulation (FQAM) and sliding window superposition coding(SWSC) as an advanced coding modulation (ACM), and filter bank multicarrier (FBMC), non-orthogonal multiple access (NOMA), and sparse codemultiple access (SCMA) as an advanced access technology have beendeveloped.

An embodiment of the present invention provides an apparatus and amethod for transmitting reference signals in a wireless communicationsystem.

Another embodiment of the present invention provides an apparatus and amethod for transmitting reference signals for Multi-User (MU)-MultipleInput and Multiple Output (MIMO) in a wireless communication system.

Yet another embodiment of the invention provides an apparatus and amethod for transmitting reference signals for MU-MIMO of a high order ina wireless communication system.

Still another embodiment of the invention provides an apparatus and amethod for improving of channel estimation performance in MU-MIMOcommunication in a wireless communication system.

A further embodiment of the invention provides an apparatus and a methodfor transmitting control information for reference signals for MU-MIMOcommunication in a wireless communication system.

A method for operating a terminal in a wireless communication systemaccording to an embodiment of the present invention includes receivingcontrol information for reference signals from a base station, andreceiving the reference signals according to the control information,wherein the control information includes information indicating a lengthof an orthogonal code applied to the reference signals.

A method for operating a terminal in a wireless communication systemaccording to another embodiment of the present invention includesreceiving control information according to control information, andperforming blind detection for the reference signals, wherein the blinddetection is performed by considering different situations for at leastone of whether reference signals for another multiplexing group aretransmitted and a power boosting value applied to the reference signals.

A method for operating a base station in a wireless communication systemaccording to an embodiment of the present invention includestransmitting control information for reference signals to a terminal,and transmitting the reference signals to the terminal according to thecontrol information, wherein the control information includesinformation indicating a length of an orthogonal code applied to thereference signals.

An apparatus of a terminal in a wireless communication system accordingto an embodiment of the present invention includes a receiving unit forreceiving control information for reference signals from a base station,and receiving the reference signals according to the controlinformation, wherein the control information includes informationindicating a length of an orthogonal code applied to the referencesignals.

An apparatus of a terminal in a wireless communication system accordingto another embodiment of the present invention includes a receiving unitfor receiving reference signals according to control information, and acontrol unit for performing blind detection for the reference signals,wherein the blind detection is performed by considering differentsituations for at least one of whether reference signals for anothermultiplexing group are transmitted and a power boosting value applied tothe reference signals.

An apparatus of a base station in a wireless communication systemaccording to an embodiment of the present invention includes atransmitting unit for transmitting control information for referencesignals to a terminal, and transmitting the reference signals to theterminal according to the control information, wherein the controlinformation includes information indicating a length of an orthogonalcode applied to the reference signals.

According to another embodiment of the present invention, the controlinformation can further include at least one of information indicatingthe number of multiplexed terminals, information indicating whetherreference signals for other multiplexing group are transmitted, a powerboosting value applied to the reference signals, a reference signalrelated parameter of a subband unit, and information indicating thenumber of subbands applying the same parameter.

Reference signals can be transmitted efficiently according to the numberof terminals multiplexed through Multi-User (MU)-Multiple Input andMultiple Output (MIMO) in a wireless communication system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an example of a base station and a terminal fortransmitting reference signals in a wireless communication systemaccording to an embodiment of the present invention.

FIG. 2 depicts a block diagram of a base station in a wirelesscommunication system according to an embodiment of the presentinvention.

FIG. 3 depicts a block diagram of a terminal in a wireless communicationsystem according to an embodiment of the present invention.

FIG. 4 depicts a mapping example of reference signals in a wirelesscommunication system according to an embodiment of the presentinvention.

FIG. 5 depicts an operating procedure of a base station in a wirelesscommunication system according to an embodiment of the presentinvention.

FIG. 6 depicts an operating procedure of a terminal in a wirelesscommunication system according to an embodiment of the presentinvention.

FIG. 7 depicts an example of a situation where four antenna ports areused for one Code Division Multiplexing (CDM) group in a wirelesscommunication system according to an embodiment of the presentinvention.

FIGS. 8A and 8B depict examples of an orthogonal code length based onthe number of terminals in a wireless communication system according toan embodiment of the present invention.

FIG. 9 depicts a reference signal transmitting procedure based oncontrol information notifying an orthogonal code length in a wirelesscommunication system according to an embodiment of the presentinvention.

FIG. 10 depicts a reference signal receiving procedure based on controlinformation notifying an orthogonal code length in a wirelesscommunication system according to an embodiment of the presentinvention.

FIGS. 11A and 11B depict another example of an orthogonal code lengthbased on the number of terminals in a wireless communication systemaccording to an embodiment of the present invention.

FIG. 12 depicts a scheduling example with a legacy terminal in awireless communication system according to an embodiment of the presentinvention.

FIG. 13 depicts an example of a situation where four antenna ports areused for two CDM groups in a wireless communication system according toan embodiment of the present invention.

FIG. 14 depicts an example of an interpretation of reference signalresources for other group in a wireless communication system accordingto an embodiment of the present invention.

FIG. 15 depicts a detecting procedure which interprets a referencesignal resource of other group as delivery of reference signals in awireless communication system according to an embodiment of the presentinvention.

FIG. 16 depicts another example of an interpretation of reference signalresources for other group in a wireless communication system accordingto an embodiment of the present invention.

FIG. 17 depicts a data processing procedure for a terminal to interpreta reference signal resource of other group as delivery of data signalsin a wireless communication system according to the present invention.

FIG. 18 depicts a detecting procedure which interprets a referencesignal resource of other group as delivery of data signals in a wirelesscommunication system according to an embodiment of the presentinvention.

FIG. 19 depicts yet another example of an interpretation of referencesignal resources for other group in a wireless communication systemaccording to an embodiment of the present invention.

FIG. 20 depicts a blind detection procedure considering a referencesignal resource of other group in a wireless communication systemaccording to an embodiment of the present invention.

FIG. 21 depicts a reference signal transmitting procedure based oncontrol information notifying a use of a reference signal resource ofother group in a wireless communication system according to anembodiment of the present invention.

FIG. 22 depicts a reference signal receiving procedure based on controlinformation notifying a use of a reference signal resource of othergroup in a wireless communication system according to an embodiment ofthe present invention.

FIGS. 23A and 23B depict power difference between reference signals anddata signals according to the number of terminals in a wirelesscommunication system according to an embodiment of the presentinvention.

FIGS. 24A and 24B depict an example of a fixed power boosting value ofreference signals in a wireless communication system according to anembodiment of the present invention.

FIG. 25 depicts blind detection in consideration of power differencebetween reference signals and data signals in a wireless communicationsystem according to an embodiment of the present invention.

FIG. 26 depicts selective blind detection in consideration of amodulation scheme in a wireless communication system according to anembodiment of the present invention.

FIG. 27 depicts a reference signal transmitting procedure based oncontrol information notifying a power boosting value in a wirelesscommunication system according to an embodiment of the presentinvention.

FIG. 28 depicts a reference signal receiving procedure based on controlinformation notifying a power boosting value in a wireless communicationsystem according to an embodiment of the present invention.

FIGS. 29A and 29B show an application example of subframe unit controlinformation in a wireless communication system according to anembodiment of the present invention.

FIG. 30 depicts a configuration of subband unit control information in awireless communication system according to an embodiment of the presentinvention.

FIG. 31 depicts a configuration of resource group unit controlinformation in a wireless communication system according to anembodiment of the present invention.

FIG. 32 depicts a reference signal transmitting procedure based oncontrol information notifying a resource group size in a wirelesscommunication system according to an embodiment of the presentinvention.

FIG. 33 depicts a reference signal receiving procedure based on controlinformation notifying a resource group size in a wireless communicationsystem according to an embodiment of the present invention.

FIGS. 34A and 34B depict a configuration of control information dividedbased on an application range in a wireless communication systemaccording to an embodiment of the present invention.

FIG. 35 depicts a reference signal transmitting procedure based oncontrol information divided based on an application range in a wirelesscommunication system according to an embodiment of the presentinvention.

FIG. 36 depicts a reference signal receiving procedure based on controlinformation divided based on an application range in a wirelesscommunication system according to an embodiment of the presentinvention.

DETAILED DESCRIPTION

Hereinafter, an operational principle of the present invention isdescribed in detail with reference to the accompanying drawings. In thefollowing explanations, well-known functions or constitutions will notbe described in detail if they would unnecessarily obscure the subjectmatter of the present invention. Also, terminologies to be describedbelow are defined in consideration of functions in the present inventionand can vary depending on a user's or an operator's intention orpractice. Thus, their definitions should be defined based on all thecontents of the specification.

Hereafter, the present invention describes a technique for transmittingand receiving reference signals in a wireless communication system.

Hereafter, terms for indicating signals, terms for indicating networkentities, terms for indicating channels, terms for identifying antennas,and terms for indicating control information or parameters in thecontrol information are used to ease the understanding. Accordingly, thepresent invention is not limited to those terms and can adopt otherterms indicating targets having technically equivalent meanings.

Hereafter, the present invention explains a wireless communicationsystem of an Orthogonal Frequency Division Multiplexing(OFDM)/Orthogonal Frequency Division Multiple Access (OFDMA) scheme byway of example. Also, to ease the understanding, terms and names definedin 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE)standard are used. However, the present invention is not limited tothose terms and names, and can be equally applied to a system conformingto other standards.

To increase system capacity of the wireless communication system,techniques for increasing and using antennas in a base station aredeveloping. A system using a large number of antennas can greatlyincrease the system capacity by facilitating Multi-User (MU)multi-antenna, that is, MU-Multiple Input and Multiple Output (MIMO)transmission through array gain. Hence, various embodiments of thepresent invention describe a structure and a design of reference signalsfor the MU-MIMO transmission.

A system such as LTE-Advanced (LTE-A) uses reference signals for channelinformation estimation of a receiving stage to receive data from atransmitting stage. Thus, a wireless communication system according toan embodiment of the present invention can use the reference signals asshown in FIG. 1.

FIG. 1 depicts an example of a base station and a terminal fortransmitting reference signals in a wireless communication systemaccording to an embodiment of the present invention. While only oneterminal is shown in FIG. 1, a plurality of terminals can receivereference signals. Referring to FIG. 1, a base station 110 and aterminal 120 can communicate. In so doing, the base station 110 cantransmit reference signals to the terminal 120. The reference signal isa signal for estimating channel information, and has a pre-arrangedvalue between the base station 110 and the terminal 120. The referencesignal can be referred to as a pilot, a training signal, and so on. Thereference signal can be referred to variously according to its use, andthe reference signal used in data reception, that is, channel estimationfor demodulation and channel decoding of data signals can be referred toas a Demodulation Reference Signal (DM-RS).

In MU-MIMO transmission, even when data resources are transmitted at thesame time to enhance a transmission rate, a reference signal resourcefor the channel estimation is required to be allocated orthogonally foraccuracy of the channel estimation. Hence, as the number of terminalsserviced in the MU-MIMO or the number of data streams increases, morereference signal resources can be consumed. Accordingly, variousembodiments of the present invention provide a reference signaltransmission and reception technique for the MU-MIMO of a higher order.

FIG. 2 depicts a block diagram of a base station in a wirelesscommunication system according to an embodiment of the presentinvention. FIG. 2 illustrates a structure of the base station 110.

As shown in FIG. 2, the base station includes a communication unit 210,a storage unit 220, and a control unit 230. Hereinafter, a term such as‘ . . . unit’, ‘ . . . part’ means a unit for processing at least onefunction or operation, which can be implemented using hardware,software, or a combination of hardware and software.

The communication unit 210 performs functions for transmitting andreceiving signals over a radio channel. For example, the communicationunit 210 performs a conversion function between a baseband signal and abit stream according to a physical layer standard of a system. Forexample, in data transmission, the communication unit 210 generatescomplex symbols by encoding and modulating a transmit bit stream. In sodoing, the communication unit 210 can map the complex symbols tosubcarriers, and generate OFDM symbols through an Inverse Fast FourierTransform (IFFT) operation. Also, in data reception, the communicationunit 210 restores a receive bit stream by demodulating and decoding abaseband signal. Also, the communication unit 210 up-converts thebaseband signal to a Radio Frequency (RF) band signal, transmits it viaan antenna, and down-converts an RF band signal received via the antennato a baseband signal. For example, the communication unit 210 caninclude a transmit filter, a receive filter, an amplifier, a mixer, anoscillator, a Digital to Analog Convertor (DAC), an Analog to DigitalConvertor (ADC), and the like.

Also, the communication unit 210 can include a plurality of RF chains.Further, the communication unit 210 can conduct beamforming. For thebeamforming, the communication unit 210 can adjust a phase and amagnitude of signals transmitted and received over a plurality ofantennas or antenna elements. Also, the communication unit 210 canprecode a plurality of data streams transmitted. Hence, the base stationcan perform the MU-MIMO communication. The communication unit 210transmits and receives the signals as mentioned above. Accordingly, thecommunication unit 210 can be referred to as a transmitting unit, areceiving unit, or a transceiving unit.

The storage unit 220 stores a basic program for the operations of thebase station, an application program, and data such as settinginformation. Also, the storage unit 220 provides the stored dataaccording to a request of the control unit 230.

The control unit 230 controls general operations of the base station.For example, the control unit 220 transmits/receives signals through thecommunication unit 210. Also, the control unit 230 records and readsdata in and from the storage unit 220. For doing so, the control unit230 can include at least one processor. According to an embodiment ofthe present invention, the control unit 230 can include a referencesignal mapping unit 232 for generating and mapping reference signals.Also, the control unit 230 can include a control information generatingunit 234 for generating control information for the reference signals.For example, the control unit 230 can control the base station totransmit the control information and the reference signals, to beexplained.

FIG. 3 depicts a block diagram of a terminal in a wireless communicationsystem according to an embodiment of the present invention. FIG. 3illustrates a structure of the terminal 120.

As shown in FIG. 3, the terminal includes a communication unit 310, astorage unit 320, and a control unit 330. Hereinafter, a term such as ‘. . . unit’, ‘ . . . part’ means a unit for processing at least onefunction or operation, which can be implemented using hardware,software, or a combination of hardware and software.

The communication unit 310 performs functions for transmitting andreceiving signals over a radio channel. For example, the communicationunit 310 performs a conversion function between a baseband signal and abit stream according to a physical layer standard of a system. Forexample, in data transmission, the communication unit 310 generatescomplex symbols by encoding and modulating a transmit bit stream. Also,in data reception, the communication unit 310 restores a receive bitstream by demodulating and decoding a baseband signal. In so doing, thecommunication unit 310 can restore the complex symbols per subcarrier bysplitting the received signal on the OFDM symbol unit and performing anFFT operation on the OFDM symbol. Also, the communication unit 310up-converts the baseband signal to an RF band signal, transmits it viaan antenna, and down-converts an RF band signal received via the antennato a baseband signal. For example, the communication unit 310 caninclude a transmit filter, a receive filter, an amplifier, a mixer, anoscillator, a DAC, an ADC, and the like.

Also, the communication unit 310 can include a plurality of RF chains.Further, the communication unit 310 can conduct beamforming. For thebeamforming, the communication unit 310 can adjust a phase and amagnitude of signals transmitted and received over a plurality ofantennas or antenna elements. The communication unit 310 transmits andreceives the signals as mentioned above. Accordingly, the communicationunit 310 can be referred to as a transmitting unit, a receiving unit, ora transceiving unit.

The storage unit 320 stores a basic program for the operations of theterminal, an application program, and data such as setting information.Also, the storage unit 320 provides the stored data according to arequest of the control unit 330.

The control unit 330 controls general operations of the terminal. Forexample, the control unit 330 transmits/receives signals through thecommunication unit 310. Also, the control unit 330 records and readsdata in and from the storage unit 320. For doing so, the control unit330 can include at least one processor. For example, the control unit330 can include a Communication Processor (CP) for controlling thecommunication and an Application Processor (AP) for controlling a higherlayer such as application program. According to an embodiment of thepresent invention, the control unit 330 can include a reference signaldetecting unit 332 for interpreting the control information for thereference signals received from the base station and analyzing thereference signals based on the control information. For example, thecontrol unit 330 can control the terminal to receive the controlinformation and the reference signals, to be explained.

FIG. 4 depicts a mapping example of reference signals in a wirelesscommunication system according to an embodiment of the presentinvention. FIG. 4 illustrates the mapping of reference signals for eightantenna ports. The antenna ports are logical antennas used for the basestation to transmit a signal, and can be greater than physical antennasof the base station in number.

Referring to FIG. 4, some of Resource Elements (REs) arranged on afrequency axis and a time axis can be allocated as a control channel(e.g., physical downlink common control channel (PDCCH)), some can beused to transmit a Common Reference Signal (CRS), and some can be usedto transmit reference signals. The reference signal is used to estimatechannel information to detect data transmitted through the correspondingantenna port. Herein, the detection embraces demodulating and channeldecoding. Accordingly, the reference signal can be precoded with thedata signal and then transmitted.

Reference signals for antenna ports 7, 8, 11, and 13 are transmitted onthe same REs. Also, reference signals for antenna ports 9, 10, 12, and14 are transmitted on the same REs. That is, the reference signals forthe antenna ports 7, 8, 11, and 13 and the reference signals for theantenna ports 9, 10, 12, and 14 are transmitted over differentresources. The reference signals for the antenna ports 7, 8, 11, and 13and the reference signals for the antenna ports 9, 10, 12, and 14transmitted over the same resources can be distinguished based on CodeDivision Multiplexing (CDM). Thus, the antenna ports 7, 8, 11, and 13transmitted over the same resources are classified to a CDM group#1, andthe antenna ports 9, 10, 12, and 14 transmitted over the differentresources are classified to a CDM group#2. The CDM group#1 and the CDMgroup#2 are sets of the antenna ports, the reference signals, or theterminals multiplexed in the same resources. To ease the understanding,the CDM group can be referred to as a group, a multiplexing group, andso on.

According to the CDM, reference signals for antenna ports in one CDMgroup are multiplied by an Orthogonal Covering Code (OCC). The OCC canbe allocated to each antenna port as shown in Table 1.

TABLE 1 Port number OCC sequence 7 [+1 +1 +1 +1] 8 [+1 −1 +1 −1] 11 [+1+1 −1 −1] 13 [+1 −1 −1 +1] 9 [+1 +1 +1 +1] 10 [+1 −1 +1 −1] 12 [−1 −1 +1+1] 14 [−1 +1 +1 −1]

In Table 1, while the same OCC sequences are applied to the antennaports 7 and 9, the antenna ports 8 and 10, the antenna ports 11 and 12,and the antenna ports 13 and 14, they can be distinguished because theyuse different REs, that is, their CDM groups are different. Thereference signals for the antenna ports in the same CDM group can bedistinguished by the OCC. For example, the antenna port 8 uses the OCCsequence [+1 −1 +1 −1]. Accordingly, the reference signal for theantenna port 8 is transmitted over REs 401, 402, 403, and 404, thereference signal transmitted over the RE 401 is multiplied by +1 andthen transmitted, the reference signal transmitted over the RE 402 ismultiplied by −1 and then transmitted, the reference signal transmittedover the RE 403 is multiplied by +1 and then transmitted, and thereference signal transmitted over the RE 404 is multiplied by +1 andthen transmitted.

Hence, by combining the number corresponding to the OCC length, that is,the reference signals received over the four REs, the terminal canidentify one reference signal value corresponding to its allocatedantenna port. In so doing, the terminal can receive control informationas shown in Table 2 and obtain information about its allocated referencesignal from the control information.

TABLE 2 One codeword Two codewords value message value message 0 1layer, port 7, n_(SCID) = 0 0 2 layers, ports 7-8, n_(SCID) = 0 1 1layer, port 7, n_(SCID) = 1 1 2 layers, ports 7-8, n_(SCID) = 1 2 1layer, port 8, n_(SCID) = 0 2 3 layers, ports 7-9 3 1 layer, port 8,n_(SCID) = 1 3 4 layers, ports 7-10 4 2 layers, ports 7-8 4 5 layers,ports 7-11 5 3 layers, ports 7-9 5 6 layers, ports 7-12 6 4 layers,ports 7-10 6 7 layers, ports 7-13 7 — 7 8 layers, ports 7-14

In Table 2, the codeword indicates a coding block, the number of layersindicates the number of ranks, and n_(SCID) denotes a scramblingsequence index. That is, the case where the 2-layer is used in onecodeword indicates that one coding blocking is divided into twotransmission units and then transmitted through two pots.

Various embodiments of the present invention can be divided into a casewhere four reference signal ports are used for one CDM group and a casewhere four reference signal ports are used for two CDM groups.Additionally, the present invention provides various embodiments fortransmitting control information of reference signals per subband.

In brief, when the four reference signal ports are used for the one CDMgroup, the OCC can be applied differently according to the number of themultiplexed terminals. When the four reference signal ports are used forthe two CDM groups, a reference signal power and data channel muting canbe applied differently according to the number of the multiplexedterminals. When the control information is configured per subband, a newResource Block (RB) size can be defined to transmit reference signalport information. Alternatively, part of the reference signal portinformation can be shared for WideBand (WB), and the rest can bedistinguished per subband (SB).

Hereafter, various embodiments for various reference signalconfigurations and control information configurations based on thenumber of CDM groups are described. In the following, to ease theunderstanding, the present invention illustrates that the antenna ports7/8/11/13 are used for one CDM group. Also, the present inventionillustrates that the antenna ports 7/8/9/10 are used for two CDM groups.However, the antenna port number can vary according to a specificembodiment.

FIG. 5 depicts an operating procedure of a base station in a wirelesscommunication system according to an embodiment of the presentinvention. FIG. 5 illustrates an operating method of the base station110.

Referring to FIG. 5, the base station transmits control information forreference signals in step 501. The control information includes controlinformation required for a terminal to detect the reference signals. Forexample, the control information can include information indicating anantenna port allocated to the terminal, and information indicating anorthogonal code (e.g., OCC). In particular, according to an embodimentof the present invention, the control information can include at leastone of information indicating an orthogonal code length, informationindicating the number of multiplexed terminals, information indicatingwhether reference signals for another group (e.g., CDM group) aretransmitted, information indicating a power boosting value applied tothe reference signals, a reference signal related parameter of a subbandunit, and information indicating the number of subbands to which thesame control information is applied. Alternatively, according to anembodiment of the present invention, the control information can bedivided into a first portion and a second portion, the first portion canbe transmitted as information corresponding to each of the plurality ofsubbands, and the second portion can be transmitted as informationcorresponding to each of the plurality of subbands.

Next, the base station transmits reference signals according to thecontrol information in step 503. In so doing, the base station cantransmit the reference signals using orthogonal codes of the lengthindicated by the control information. Alternatively, the base stationcan mute a data resource for a second group with respect to REs carryingreference signals for a first group. Alternatively, the base station canboost the reference signals according to the value indicated by thecontrol information.

FIG. 6 depicts an operation procedure of a terminal in a wirelesscommunication system according to an embodiment of the presentinvention. FIG. 6 illustrates an operating method of the terminal 120.

Referring to FIG. 6, the terminal receives control information forreference signals in step 601. The control information includes controlinformation required for the terminal to detect the reference signals.For example, the control information can include information indicatingan antenna port allocated to the terminal, and information indicating anorthogonal code (e.g., OCC). In particular, according to an embodimentof the present invention, the control information can include at leastone of information indicating the orthogonal code length, informationindicating the number of multiplexed terminals, information indicatingwhether reference signals for another group (e.g., CDM group) aretransmitted, information indicating a power boosting value applied tothe reference signals, a reference signal related parameter on thesubband unit, and information indicating the number of subbands to whichthe same control information is applied to. Alternatively, according toan embodiment of the present invention, the control information can bedivided into a first portion and a second portion, the first portion canbe received as information corresponding to each of the plurality ofsubbands, and the second portion can be received as informationcorresponding to each of the plurality of subbands.

Next, the terminal receives reference signals according to the controlinformation in step 603. In so doing, the terminal can detect thereference signals for the antenna ports allocated to the terminal usingorthogonal codes of the length indicated by the control information.Alternatively, the terminal can interpret that REs carrying referencesignals for another group are empty or carry data signals, or performblind detection. Alternatively, the terminal can detect the referencesignals by considering a power boosting value indicated by the controlinformation. Alternatively, the terminal can obtain the controlinformation for the terminal by combining the first portion applied tothe plurality of the subbands and the second portion applied to eachsubband.

Embodiments when four reference signal ports are used for one CDM groupare as follows. To describe the case where the four reference signalports are used for the one CDM group, a situation of FIG. 7 isillustrated.

FIG. 7 depicts an example of a situation where four antennas are usedfor one CDM group in a wireless communication system according to anembodiment of the present invention. Referring to FIG. 7, a base station110 communicates with terminals 120-1 through 120-4. In so doing, theterminal 120-1 uses an antenna port 7, the terminal 120-2 uses anantenna port 8, the terminal 120-3 uses an antenna port 11, and theterminal 120-4 uses an antenna port 13.

The base station 110 transmits control information for referencesignals, that is, control information to the terminals 120-1 through120-4. The control information indicates the number of layers allocatedto each terminal, that is, the number of streams or ports, and theallocated port number. For example, the control information can beconfigured as shown in Table 3.

TABLE 3 value note 0 1 layer, port 7 1 1 layer, port 8 2 1 layer, port11 3 1 layer, port 13

In Table 3, ‘value’ is the value transmitted as the control information,and ‘contents’ is a corresponding parameter.

The terminals 120-1 through 120-4 receiving the control informationapply the orthogonal code corresponding to the allocated antenna port,that is, the OCC. For example, correspondence between the antenna portand the orthogonal code can be defined as shown in Table 4.

TABLE 4 Port number Orthogonal code 7 [+1 +1 +1 +1] 8 [+1 −1 +1 −1] 11[+1 +1 −1 −1] 13 [+1 −1 −1 +1]

Referring to the orthogonal codes in Table 4, it is noted that just someof the orthogonal codes have orthogonality. In particular, theorthogonal codes allocated to the port 7 and the port 8 have theorthogonality merely with two values as shown in Table 5.

TABLE 5 Port number Orthogonal code 7 [+1 +1 +1 +1] → [+1 +1] 8 [+1 −1+1 −1] → [+1 −1]

The length of the orthogonal code for the CDM is greatly related tochannel estimation performance. That is, as the length of the orthogonalcode gets short, the number of resources (e.g., REs) to use to maintainthe orthogonality reduces. The number of the resources reduces, morevalid reference signals can be provided and thus the channel estimationperformance can be enhanced. Hence, when only the port 7 and the port 8are used, it is preferred to enhance the channel estimation performanceby applying orthogonal codes of the length 2. Thus, a system accordingto an embodiment of the present invention can use orthogonal codes ofdifferent lengths according to the number of the multiplexed terminalsin the same resource as shown in FIG. 8A and FIG. 8B.

FIGS. 8A and 8B depict examples of an orthogonal code length based onthe number of terminals in a wireless communication system according toan embodiment of the present invention. In FIGS. 8A and 8B, an arrowindicates a range of REs applying one orthogonal code. FIG. 8A shows acase where two terminals are multiplexed in the same resource, that is,two terminals are included in one CDM group. In this case, sincereference signals for two ports (e.g., ports 7 and 8) can haveorthogonality according to the orthogonal codes of the length 2, theorthogonal codes of the length 2 can be used. FIG. 8B shows a case wherefour terminals are multiplexed in the same resource, that is, fourterminals are included in one CDM group. In this case, since referencesignals for four ports (e.g., ports 7, 8, 11, and 13) cannot have theorthogonality according to the orthogonal codes of the length 2, theorthogonal codes of length 4 are used.

As stated above, the length of the orthogonal code can vary according tothe number of the terminals. In this case, information about theorthogonal code length to be applied by the terminals needs to betransmitted to the terminals. More specifically, the base station needsto inform the terminals of whether to apply the orthogonal code length 2or the orthogonal code length 4. For doing so, the present inventionsuggests a reference signal port using method to transmit the orthogonalcode length in addition to the existing reference signal portinformation. Herein, since the length depends on the number of thereference signals multiplexed in the same resource, the reference signalor terminal number information can replace the orthogonal code length.

According to an embodiment of the present invention, the orthogonal codelength can be added to the control information of the reference signals.However, since the situation where the orthogonal codes of the length 2are limited, the control information can be configured more efficiently.When one CDM group uses only two of the four ports, the orthogonal codelength 2 can be applied. Hence, the present invention suggests a controlinformation structure which can change the orthogonal code length onlyfor particular ports. For example, the control information can beconfigured as shown in Table 6.

TABLE 6 Value Port Lengh of orthogonal code 0 port 7 2 1 port 8 2 2 port7 4 3 port 8 4 4 port 11 4 5 port 13 4

In Table 6, ‘value’ is the value transmitted as the control information,and ‘port’ and ‘orthogonal code length’ are corresponding parameters. Asshown in Table 6, two orthogonal code lengths (e.g., 2 or 4) can beselected only for the port 7 and the port 8. This is because the use ofthe ports 11 and 13 means that three or more terminals are multiplexed.

The information indicating the port and the orthogonal code lengthrepresentable as shown in Table 6 can be delivered together with otherinformation. For example, the control information can further indicatethe number of layers, a scrambling sequence index, and the like. In thiscase, the control information according to an embodiment can beconfigured by further adding the orthogonal cod length to the controlinformation constructed as shown in Table 1.

FIG. 9 depicts a reference signal transmitting procedure based oncontrol information notifying an orthogonal code length in a wirelesscommunication system according to an embodiment of the presentinvention. FIG. 9 illustrates an operating method of the base station110.

Referring to FIG. 9, the base station transmits control informationindicating an orthogonal code length in step 901. Herein, the orthogonalcode length can vary according to the number of terminals multiplexed inthe same resource, that is, participating in MU-MIMO transmission.Hence, the base station determines the orthogonal code length based onthe number of the terminals participating in the MU-MIMO transmission,and transmits the control information indicating the orthogonal codelength. For example, the control information can include informationexplicitly indicating the orthogonal code length, or informationnotifying the number of the terminals participating in the MU-MIMOtransmission.

Next, the base station transmits reference signals multiplexed using theorthogonal codes in step 903. That is, the base station transmits thereference signals using the orthogonal codes having the orthogonal codelength indicated by the control information. More specifically, the basestation can generate the reference signals for a plurality of terminalsby multiplying the orthogonal codes to a set of reference signals, andtransmit the reference signals over the same resource.

FIG. 10 depicts a reference signal receiving procedure based on controlinformation notifying an orthogonal code length in a wirelesscommunication system according to an embodiment of the presentinvention. FIG. 10 illustrates an operating method of the terminal 120.

Referring to FIG. 10, the terminal receives control informationindicating an orthogonal code length in step 1001. Herein, theorthogonal code length can vary according to the number of terminalsmultiplexed in the same resource, that is, participating in MU-MIMOtransmission. For example, the control information can includeinformation explicitly indicating the orthogonal code length, orinformation notifying the number of the terminals participating in theMU-MIMO transmission.

Next, the terminal receives reference signals multiplexed using theorthogonal codes in step 1003. Hence, the terminal can obtain channelinformation by multiplying the orthogonal code corresponding to areference signal port allocated to it, and the received referencesignals. In so doing, the terminal multiplies the orthogonal code of thelength indicated by the control information.

When the orthogonal code length is dynamically changed as shown in theembodiment of FIG. 8A and FIG. 8B, the channel estimation performancecan be enhanced. However, overhead of the control information increases.Hence, according to another embodiment of the present invention,orthogonal codes of the same length can be used all the time as shown inFIG. 11A and FIG. 11B.

FIGS. 11A and 11B depict another example of an orthogonal code lengthbased on the number of terminals in a wireless communication systemaccording to an embodiment of the present invention. In FIGS. 11A and11B, an arrow indicates a range of REs applying one orthogonal code.FIG. 11A shows a case where two terminals are multiplexed in the sameresource, that is, two terminals are included in one CDM group.Referring to FIGS. 11A and 11B, unlike the embodiment of the FIGS. 8Aand 8B, orthogonal codes of length 4 are used regardless of the numberof the terminals. Accordingly, a process for notifying the orthogonalcode length is not required, and overhead of control information isrelatively less.

As stated above, by using the orthogonal codes of the length 4 in oneCDM group, MU-MIMO transmission to up to 4 terminals can be performed.In so doing, when one legacy terminal is included in the four terminals,available orthogonal codes can be limited. Herein, the legacy terminalindicates a terminal not capable of interpreting the orthogonal code ofthe length 4. When the legacy terminal is multiplexed together,orthogonal code allocation can be limited as shown in FIG. 12.

FIG. 12 depicts a scheduling example with a legacy terminal in awireless communication system according to an embodiment of the presentinvention. FIG. 12 shows a case where a legacy terminal 130 is included.Referring to FIG. 12, an antenna port 7 is allocated to the legacyterminal 130. In so doing, the legacy terminal 130, which cannotinterpret an orthogonal code of length 4, uses an orthogonal code [+1+1] of length 2. When the orthogonal code allocated to the terminal 130is extended to length 4, the orthogonal code becomes [+1 +1 +1 +1].Accordingly, other available orthogonal codes of the length 4 are [+1 −1+1 −1], [+1 +1 −1 −1], and [+1 −1 −1 +1]. However, since the legacyterminal 130 interprets the orthogonal code length as 2, the orthogonalcode without orthogonality in the range of the length 2 cannot be usedtogether. That is, [+1 +1−1 −1] cannot be used. In other words, a basestation 110 cannot allocate an antenna port 11 using the orthogonal code[+1 +1 −1 −1]. Thus, for MU-MIMO transmission to terminals including thelegacy terminal 130, the base station allocates only the otherorthogonal codes excluding the orthogonal code (e.g., [+1 +1]) allocatedto the legacy terminal 130 and the orthogonal code (e.g., [+1 +1 −1 −1])having no orthogonality in the range of the length 2. As a result, inthe MU-MIMO transmission to the terminals including the legacy terminal130, the available orthogonal codes are limited and accordingly thenumber of the terminals allowing the MU-MIMO transmission reduces.

As stated above, the legacy terminal 130 cannot interpret the orthogonalcode of the length 4. Further, the legacy terminal 130 also cannotinterpret the control information indicating the orthogonal code lengthas shown in Table 6. Hence, for the legacy terminal 130, the basestation 110 can transmit the control information (e.g., Table 2) notindicating the orthogonal code length. In this case, since theinterpretation of the control information varies according to the valuecontained in the control information, it is preferred to negotiate inadvance about of which configuration the control information is used.Thus, through signaling with a higher layer, the base station can notifyof whether the control information including the orthogonal code lengthinformation is transmitted or the control information not including theorthogonal code length information is transmitted.

Embodiments for a case where four reference signal ports are used fortwo CDM groups are as below. To explain the case where the fourreference signal ports are used for the two CDM groups, a situation ofFIG. 13 is illustrated.

FIG. 13 depicts an example of a situation where four antenna ports areused for two CDM groups in a wireless communication system according toan embodiment of the present invention. Referring to FIG. 13, a basestation 110 communicates with terminals 120-1 through 120-4. In sodoing, the terminal 120-1 uses an antenna port 7, the terminal 120-2uses an antenna port 8, the terminal 120-3 uses an antenna port 9, andthe terminal 120-4 uses an antenna port 10. The antenna ports 7 and 8belong to a first CDM group, and the antenna ports 9 and 10 belong to asecond CDM group.

That is, to support MU-MIMO transmission for the four terminals, fourorthogonal reference signal ports are needed. For doing so, two CDMgroups can be used, and the reference signal ports 7/8/9/10 can be usedas shown in FIG. 13. In this case, since two CDM groups are used, thenumber of the CDM groups used can vary according to the number of theterminals for the MU-MIMO. For example, when the terminal 120-1 and theterminal 120-2 communicate using the MU-MIMO, the second CDM group isnot required. By contrast, when all of the terminal 120-1, the terminal120-2, the terminal 120-3, and the terminal 120-4 communicate using theMU-MIMO, both of the first CDM group and the second CDM group arerequired. When the number of the CDM groups varies, data channel (e.g.,Physical Downlink Shared Channel (PDSCH)) mapping can change or a powerboosting value for the reference signals can change.

A data channel mapping problem according to the use of the two CDMgroups are as follows. Referring to FIG. 13, the MU-MIMO transmissionfor the terminals 120-1 through 120-4 is supported through the two CDMgroups. The terminal 120-1 belongs to the first CDM group and uses theantenna port 7, the terminal 120-2 belongs to the first CDM group anduses the antenna port 8, the terminal 120-3 belongs to the second CDMgroup and uses the antenna port 9, and the terminal 120-4 belongs to thesecond CDM group and uses the antenna port 10. At this time, hatched REsare resource for delivering reference signals for a terminal belongingto other CDM group, and need to be determined by each terminal. Morespecifically, it can be ambiguous for the terminal 120-1 belonging tothe first CDM group to determine whether to interpret REs carrying thereference signals of the second CDM group as the reference signals forthe terminals 120-3 and 120-4 belonging to the second CDM group or itsdata. That is, the interpretation on the data signal mapping can beambiguous. The terminals 120-3 and 120-4 belonging to the second CDMgroup can be also subject to similar ambiguity.

Thus, the present invention suggests embodiments which i) interprets asreference signal transmission, ii) interprets as data signaltransmission, or iii) interprets in consideration of both cases in REswhich can carry reference signals of other CDM group.

The case where the REs for delivering the reference signals of the otherCDM group transmit the reference signals is illustrated in FIG. 14. Thatis, as shown in FIG. 14, each terminal can assume a CDM group notallocated to it as a reference signal port of other terminals.

FIG. 14 depicts an example of an interpretation of reference signalresources for other group in a wireless communication system accordingto an embodiment of the present invention. In FIG. 14, REs marked with‘x’ are interpreted as empty REs by a corresponding terminal. Referringto FIG. 14, a base station 110 performs MU-MIMO transmission to fourterminals 120-1 through 120-4. In so doing, the terminals 120-1 through120-4 interpret data signal mapping that data signals are not mapped tothe REs carrying the reference signals of the other CDM group. Hence,the terminals 120-1 through 120-4 exclude REs carrying the referencesignals of its CDM group and the other CDM group, and detect signalsreceived on other REs. The interpretation of FIG. 14 estimates thereference signal port of other terminal, which can be advantageous in areceiving device design for controlling interference between terminalsoccurring in the MU-MIMO transmission. In the interpretation of FIG. 14,the terminals 120-1 through 120-4 each can operate as shown in FIG. 15.

FIG. 15 depicts a detection procedure for interpreting a referencesignal resource of other group as delivering reference signals in awireless communication system according to an embodiment of the presentinvention. FIG. 15 illustrates an operating method of the terminal 120.

Referring to FIG. 15, the terminal receives a symbol including referencesignals in step 1501. Some REs of the symbol include the referencesignals, and some REs include data signals. At this time, some REs ofthe symbol include at least one RE for carrying reference signals ofother group.

Next, the terminal interprets at least one RE for transmitting thereference signals of the other group as empty, and detects data in step1503. That is, the terminal interprets at least one RE allocable for thereference signals of the other group as empty, and detects the data.That is, the terminal tries to detect data by excluding at the at leastone REs and demodulating and decoding signals received on other REs.

As an another embodiment of FIG. 14, a case where REs for deliveringreference signals of other CDM group transmit data signals isillustrated in FIG. 16. That is, as shown in FIG. 16, each terminal canassume a CDM group not allocated to it as its data channel.

FIG. 16 depicts another example of an interpretation of reference signalresources for other group in a wireless communication system accordingto an embodiment of the present invention. Referring to FIG. 16, a basestation 110 performs MU-MIMO transmission to four terminals 120-1through 120-4. In so doing, the terminals 120-1 through 120-4 interpretdata signal mapping that data signals are mapped to the REs fordelivering reference signals of other CDM group. Hence, the terminals120-1 through 120-4 detect signals received on REs including resourcesfor carrying reference signals of its allocated CDM group and anotherCDM group. While the terminals 120-1 through 120-4 interpret a CDM groupnot allocated to it as a data channel, the base station 110 can applydata channel muting in a corresponding RE and utilize for the referencesignal transmission for other terminal. In this case, while theterminals 120-1 through 120-4 interpret a corresponding RE as the datachannel, they receive a signal which actually causes an error, that is,a reference signal for other terminal and thus data detectionperformance can degrade. Accordingly, in consideration of such asituation, the base station 110 can aid in the successful detection bypre-adjusting a Modulation and Coding Scheme (MCS) level applied to thedata destined for the terminals 120-1 through 120-4. In theinterpretation of FIG. 16, the base station 110 can operate as show inFIG. 17 and the terminals 120-1 through 120-4 each can operate as shownin FIG. 18.

FIG. 17 depicts a data processing procedure for a terminal whichinterprets a reference signal resource of other group as delivering datasignals in a wireless communication system according to the presentinvention. FIG. 17 illustrates an operating method of the base station110.

Referring to FIG. 17, the base station excludes at least one RE carryingreference signals of a first group from REs for data delivery of asecond group in step 1701. That is, the base station allocates aresource for the data transmission of the second group in a range ofother REs excluding at least one RE carrying the reference signals ofthe first group.

Next, the base station lowers an MCS level of the second group in step1703. According to this embodiment, a terminal belonging to the secondgroup interprets that data signals to the terminal are mapped to the atleast one RE carrying the reference signals of the first group. However,since the data signals are not mapped to the at least one RE, adetection error probability of the terminal increases. Hence, the basestation can conduct more coding and modulation by lowering the MCS levelso as to overcome the detection error probability increase due to the atleast one RE.

FIG. 18 depicts a detection procedure which interprets a referencesignal resource of other group as delivery of data signals in a wirelesscommunication system according to an embodiment of the presentinvention. FIG. 18 illustrates an operating method of the terminal 120.

Referring to FIG. 18, the terminal receives a symbol including referencesignals in step 1801. Some REs of the symbol include the referencesignals, and some REs include data signals. At this time, some REs ofthe symbol include at least one RE for carrying reference signals ofother group.

Next, the terminal interprets that data signals are mapped to at leastone RE for carrying the reference signals of the other group, anddetects data in step 1803. That is, the terminal detects data byinterpreting that at least one data signal for the terminal is mapped toat least one RE allocable for the reference signals of the other group.That is, the terminal tries the data detection by demodulating anddecoding signals received over a plurality of REs including the at leastone RE. In so doing, when the reference signals for the other group aremapped to the at least one RE, a detection error can occur.

As yet another embodiment of FIG. 14 and FIG. 16, blind detection isperformed on REs for carrying reference signals of other CDM group inFIG. 19. That is, as shown in FIG. 19, depending on the blind detection,each terminal can interpret a reference signal resource of a CDM groupnot allocated to it.

FIG. 19 depicts yet another example of an interpretation of referencesignal resources for other group in a wireless communication systemaccording to an embodiment of the present invention. Referring to FIG.19, the terminals 120-1 through 120-4 receive a signal withoutinformation about reference signal port mapping conducted by a basestation 110. That is, the base station 110 adjusts the number of CDMgroups according to the number of the terminals, and the terminals 120-1through 120-4 can repeat detection corresponding to every possiblesituation and then determine that a situation corresponding to thesuccessful detection as the reference signal port mapping conducted bythe base station 110. More specifically, as first detection, theterminals 120-1 through 120-4 exclude REs for carrying reference signalsof their allocated CDM group and other CDM group and detect a signalreceived over other REs. As second detection, the terminals 120-1through 120-4 detect a signal received over REs including resources forcarrying the reference signals of their allocated CDM group and theother CDM group. Next, the terminals 120-1 through 120-4 can select adetection result successfully decoded without error during the primarydetection and the secondary detection as a final detection result. Inthe interpretation of FIG. 19, the terminals 120-1 through 120-4 eachcan operate as shown in FIG. 20.

FIG. 20 depicts a blind detection procedure considering a referencesignal resource of other group in a wireless communication systemaccording to an embodiment of the present invention. FIG. 20 illustratesan operating method of the terminal 120.

Referring to FIG. 20, the terminal receives a symbol including referencesignals in step 2001. Some REs of the symbol include the referencesignals, and some REs include data signals. At this time, some REs ofthe symbol include at least one RE for carrying reference signals ofother group.

Next, the terminal interprets at least one RE for transmitting thereference signals of the other group as empty, and detects data in step2003. That is, the terminal tries to detect data by excluding the atleast one REs and demodulating and decoding signals received on otherREs.

Next, the terminal interprets that data signals are mapped to at leastone RE for carrying reference signals of the other group, and detectsdata in step 2005. That is, the terminal tries to detect data bydemodulating and decoding signals received over a plurality of REsincluding the at least one RE.

Next, the terminal selects an error-free detection result in step 2007.That is, in the step 2003 and the step 2005, the terminal performed thedetection twice while not knowing which signals are mapped to the atleast one RE for carrying the reference signals of the other group.Accordingly, the terminal can determine a signal corresponding to thesuccessful detection as the signal transmitted by the base station, andadopt a corresponding detection result. For example, the error can bedetermined by Cyclic Redundancy Check (CRC).

In the embodiment of FIG. 20, the terminals 120-1 through 120-4 performthe blind detection regardless of the allocated antenna port. However,according to still another embodiment of the present invention, theterminals 120-1 through 120-4 can selectively conduct the blinddetection according to the allocated antenna port or the CDM group. Thatis, the terminals 120-1 through 120-4 can perform the blind detectiononly when a particular port is allocated. For example, when a port 9 or10 of a second CDM group is allocated, the terminal can interpret afirst CDM group as reference signals. This is because the use of theport 9/10 means that the first CDM group is allocated. By contrast, whena port 7 or 8 of the first CDM group is allocated, the terminaldetermines whether another CDM group is used as reference signals foranother terminal or as its data channel through the blind detection.

As still another embodiment of FIG. 14, FIG. 16, and FIG. 19, controlinformation notifying of whether the REs for carrying the referencesignals of the other CDM group transmit reference signals or datasignals can be provided. That is, the base station can inform of whetheror not other CDM group is used, using the control information. Forexample, the control information can be transmitted through a RadioResource Control (RRC) signal of long duration, or through a controlchannel (e.g., PDCCH) per subframe. In this case, the base station canoperate as shown in FIG. 21, and the terminal can operate as shown inFIG. 22.

FIG. 21 depicts a reference signal transmitting procedure based oncontrol information notifying use of a reference signal resource ofother group in a wireless communication system according to anembodiment of the present invention. FIG. 21 illustrates an operatingmethod of the base station 110.

Referring to FIG. 21, the base station transmits control informationnotifying of whether reference signals of other group are transmitted instep 2101. The control information can be transmitted through an RRCmessage or in the form of Downlink Control Information (DCI) over acontrol channel of a subframe. That is, the control information notifiesa terminal belonging to a first group of whether reference signals for asecond group are transmitted, and notifies a terminal belonging to asecond group of whether reference signals for the first group aretransmitted.

Next, the base station transmits a symbol including the referencesignals in step 2103. Some REs of the symbol include the referencesignals, and some REs include data signals. In so doing, some REs of thesymbol include at least one RE for delivering reference signals of othergroup. If the control information indicates the transmission of thereference signals of the other group, the reference signals for theother group are mapped to the at least one RE. When the controlinformation indicates no transmission of the reference signals of theother group, the data signals for the group are mapped to the at leastone RE.

FIG. 22 depicts a reference signal receiving procedure based on controlinformation notifying use of a reference signal resource of other groupin a wireless communication system according to an embodiment of thepresent invention. FIG. 22 illustrates an operating method of theterminal 120.

Referring to FIG. 22, the terminal receives control informationnotifying of whether reference signals of other group are transmitted instep 2201. The control information can be transmitted through an RRCmessage or as DCI over a control channel of a subframe. That is, thecontrol information notifies a terminal belonging to a first group ofwhether reference signals for a second group are transmitted, andnotifies a terminal belonging to the second group of whether referencesignals for the first group are transmitted. For example, the controlinformation can explicitly indicate whether the reference signals forthe other group (e.g., the first group or the second group) aretransmitted, or whether muting is applied to a data channel of acorresponding group.

Next, the terminal receives a symbol including the reference signals instep 2203. Some REs of the symbol include the reference signals, andsome REs include data signals. In so doing, some REs of the symbolinclude at least one RE for delivering the reference signals of theother group. If the control information indicates the transmission ofthe reference signals of the other group, the terminal interprets thatthe reference signals for the other group are mapped to the at least oneRE. If the control information indicates no transmission of thereference signals of the other group, the terminal interprets that datasignals for the terminal are mapped to the at least one RE.

Next, the terminal detects data according to the control information instep 2205. If the control information indicates the transmission of thereference signals of the other group, the terminal interprets the atleast one RE as empty, and detects the data. That is, the terminal triesto detect the data by excluding the at least one REs and demodulatingand decoding signals received on other REs. By contrast, when thecontrol information indicates no transmission of the reference signalsof the other group, the terminal interprets that the data signals aremapped to the at least one RE, and detects the data. That is, theterminal tries the data detection by demodulating and decoding signalsreceived on a plurality of REs including the at least one REs.

When four reference signals ports are used for two CDM groups, there isanother problem about the power difference between the reference signalsand the data signals besides the problem about the aforementionedinterpretation of the reference signals for the other group. That is,when four orthogonal reference signals are supported using two CDMgroups, yet another problem is that a power boosting value of thereference signals can change. Specifically, the power boosting problemis shown in FIGS. 23A and 23B.

FIGS. 23A and 23B depict power difference between reference signals anddata signals according to the number of terminals in a wirelesscommunication system according to an embodiment of the presentinvention. FIG. 23A shows MU-MIMO transmission to two terminals 120-1and 120-2, and FIG. 23B shows MU-MIMO transmission to four terminals120-1 through 120-4.

Referring to FIG. 23A, when only one CDM group is used, two referencesignals are multiplexed and two data signals are multiplexed in the sameresource. That is, since the number of the reference signals and thenumber of the data signals transmitted on the same resource are thesame, a difference of a reference signal power and a data channel powerin MU-MIMO transmission can be 0 dB.

However, as shown in FIG. 23B, when two CDM groups are used, tworeference signals are multiplexed and four data signals are multiplexedin the same resource. That is, since the number of the data signalstransmitted on the same resource is greater than the number of thereference signals. Accordingly, the data signals can be transmitted with¼ power of an available power, and the reference signals can betransmitted with ½ power of the available power. As a result, when twoCDM groups are used, the reference signal power can be greater than thedata signal by 3 dB. In this case, for accurate channel estimation, thebase station 110 needs to transmit power boosting information of thereference signals to the terminals 120-1 through 120-4.

That is, as shown in FIGS. 23A and 23B, the power difference between thereference signals and the data signals can differ according to thenumber of the terminals participating in the MU-MIMO transmission. Thatis, for a terminal allocated a port 7/8, since two power differences of0 dB or 3 dB can exhibit, the power boosting value of the referencesignals needs to be determined.

As an embodiment of the power boosting value, the power differencebetween the reference signals and the data signals is fixed in FIGS. 24Aand 24B. FIGS. 24A and 24B depict an example of a fixed power boostingvalue of reference signals in a wireless communication system accordingto an embodiment of the present invention.

Referring to FIGS. 24A and 24B, the power boosting value of thereference signals can be fixed to 0 dB as shown in FIG. 24A or to 3 dBas shown in FIG. 24B. In FIG. 24A, while MU-MIMO transmission isconducted to four terminals 120-1 through 120-4, since the powerboosting value is fixed to 0 dB, a base station 110 transmits referencesignals with half power of the available power. In FIG. 24B, whileMU-MIMO transmission is conducted to two terminals 120-1 and 120-2,since the power boosting value is fixed to 3 dB, a base station 110transmits reference signals with double power of the available power.

The power boosting value can be fixed as shown in FIGS. 24A and 24B.However, the power boosting value is fixed regardless of the number ofthe terminals, and can change as time passes. That is, in terms ofmanagement of the power boosting value, the power boosting value can befixed in the system. Alternatively, the base station 110 can select thepower boosting value from 0 dB or 3 dB, and transmit the power boostingvalue through an RRC signal delivered in long duration. Alternatively,the base station 110 can transmit the power boosting value over acontrol channel (e.g., PDCCH, ePDCCH) of a subframe allocating aresource to a corresponding terminal.

As another embodiment of the power boosting value, the determination ofthe power boosting value can rely on blind detection of the terminal.That is, the base station adjusts the power boosting value for thereference signals according to the number of the terminal participatingin the MU-MIMO, and the terminal repeatedly performs the detection basedon every possible reception situation and then determines a powerboosting value corresponding to successful reception as the powerboosting value applied by the base station. In this case, the terminalcan operate as shown in FIG. 25.

FIG. 25 depicts blind detection in consideration of power differencebetween reference signals and data signals in a wireless communicationsystem according to an embodiment of the present invention. FIG. 25illustrates an operating method of the terminal 120.

Referring to FIG. 25, the terminal receives a symbol including referencesignals in step 2501. Some REs of the symbol include the referencesignals, and some REs include data signals.

Next, the terminal interprets as the same power of the data signals andthe reference signals and detects data in step 2503. In other words, theterminal interprets a power boosting value of the reference signals as 0dB. That is, the terminal applies a size of channel informationestimated through the reference signals to equalization of the datasignals without scaling, demodulates and decodes the data signals, andthus attempts the data detection. Namely, the terminal compensates fordistortion of the data signals using the channel information as it is.

Next, the terminal differently interprets the powers of the data signalsand the reference signals, and detects data in step 2505. For example,the terminal interprets the power boosting value of the referencesignals as 3 dB. That is, the terminal scales the size of the channelinformation estimated through the reference signals, applies the scaledchannel information to the equalization of the data signals, demodulatesand decodes the data signals, and thus attempts the data detection.Namely, the terminal compensates for distortion of the data signalsusing the channel information of the size adjusted according to thepower boosting value.

Next, the terminal selects an error-free detection result in step 2507.That is, in the step 2503 and the step 2505, the terminal conducts thedetection twice without knowing the power difference of the referencesignals and the data signals, that is, the power boosting value appliedto the reference signals. Hence, the terminal can determine the powerboosting value corresponding to the successful detection as the powerboosting value applied by the base station, and adopt a correspondingdetection result. For example, the error can be determined using CRC.

As in the embodiment of FIG. 25, the terminal can determine the powerboosting value applied to the reference signals through the blinddetection. However, the power boosting value is not always necessary.The effect of the power boosting value can vary according to amodulation scheme. For example, a modulation scheme which distinguishescomplex symbols merely with the phase may not be greatly affected in thesignal size. Thus, according to another embodiment of the presentinvention, selective blind detection of FIG. 26 is feasible.

FIG. 26 depicts selective blind detection in consideration of amodulation scheme in a wireless communication system according to anembodiment of the present invention. FIG. 26 illustrates a case wherequadrature phase shift Keying (QPSK), 16 quadrature amplitude modulation(QAM), and 64QAM are used as the modulation scheme. Referring to FIG.26, since the QPSK is the modulation scheme using only the phase, whenthe QPSK is used, a terminal can assume a power boosting value as 0 dB.Alternatively, the terminal can assume the power boosting value as 3 dB.That is, when a modulation scheme applied to data signals transmitted tothe terminal does not use the magnitude (e.g., when applying the QPSK),the terminal can interpret the power boosting value as a predefinedvalue and not perform the blind detection. The 16QAM and the 64QAM arethe modulation schemes using the phase and the magnitude, when the 16QAMand the 64QAM are used, the terminal performs the blind detectionconsidering a plurality of power boosting values.

That is, according to the embodiment of FIG. 26, the terminal determineswhether to conduct the blind detection according to the MCS levelallocated to it. When the blind detection is unnecessary, that is, whenthe modulation scheme (e.g., QPAK, Binary Phase Shift Keying (BPSK))using only the phase is used, the terminal interprets and detects thepower booting value as a single value. By contrast, when the blinddetection is necessary, that is, when the modulation scheme (e.g.,16QAM, 64QAM, 124QAM) using the phase and the magnitude is used, theterminal performs a procedure of FIG. 25.

As another embodiment for the power boosting value, control informationnotifying the power boosting value applied to the reference signals canbe provided. That is, the base station can notify the power boostingvalue through the control information. For example, the controlinformation can be transmitted through an RRC signal of long duration ora control channel (e.g., PDCCH) per subframe. In this case, the basestation can operate as shown in FIG. 27, and the terminal can operate asshown in FIG. 28.

FIG. 27 depicts a reference signal transmitting procedure based oncontrol information notifying a power boosting value in a wirelesscommunication system according to an embodiment of the presentinvention. FIG. 27 illustrates an operating method of the base station110.

Referring to FIG. 27, the base station transmits control informationindicating a power boosting value applied to reference signals in step2701. Herein, the power boosting value indicates a power differencebetween reference signals and data signals. The power boosting value canvary according to the number of terminals multiplexed in the sameresource, that is, participating in MU-MIMO transmission. Hence, thebase station determines the power boosting value based on the number ofthe terminals participating in the MU-MIMO transmission, and transmitsthe control information indicating the power boosting value. Forexample, the control information can include information explicitlyindicating the power boosting value, or information notifying the numberof the terminals participating in the MU-MIMO transmission.

Next, the base station transmits reference signals in step 2703. In sodoing, the base station transmits the reference signals with powercorresponding to the power boosting value. That is, the base stationadjusts the power of the reference signals according to the powerboosting value indicated by the control information.

FIG. 28 depicts a reference signal receiving procedure based on controlinformation notifying a power boosting value in a wireless communicationsystem according to an embodiment of the present invention. FIG. 28illustrates an operating method of the terminal 120.

Referring to FIG. 28, the terminal receives control informationindicating a power boosting value applied to reference signals in step2801. Herein, the power boosting value indicates a power differencebetween reference signals and data signals. The power boosting value canvary according to the number of terminals multiplexed in the sameresource, that is, participating in MU-MIMO transmission. For example,the control information can include information explicitly indicatingthe power boosting value, or information notifying the number of theterminals participating in the MU-MIMO transmission.

Next, the terminal receives reference signals and data signals in step2803. In so doing, the base station transmits the reference signals withpower corresponding to the power boosting value. That is, the referencesignals are transmitted with the power adjusted according to the powerboosting value indicated by the control information. In other words, thereference signals and the data signals are transmitted with a powerlevel corresponding to the power boosting value.

Next, the terminal detects data according to the control information instep 2805. If the control information indicates the same power of thereference signals and the data signals, the terminal interprets the samepower of the reference signals and the data signals and detects data. Inother words, the terminal interprets the power boosting value of thereference signals as 0 dB, and applies a size of channel informationestimated through the reference signals to equalization of the datasignals without scaling. By contrast, when the control informationindicates different powers of the reference signals and the datasignals, the terminal interprets different powers of the data signalsand the reference signals and detects data. For example, the terminalinterprets the power boosting value of the reference signals as 3 dB,scales the size of the channel information estimated through thereference signals, and then applies the scaled channel information tothe equalization of the data signals.

As mentioned above, when two CDM groups are used, data channel muting byreference signals of other group or the power boosting value of thereference signals can be provided as the control information. Further,the data channel muting and the power boosting value can be providedtogether. For example, when the terminal uses other CDM group as itsdata channel, the terminal can interpret the power boosting value as 0dB. Similarly, when the terminal uses other CDM group as a referencesignal port for other terminal, the terminal can interpret the powerboosting value as 3 dB. Additionally, the control informationconfiguration as described above can be applied only to a particularreference signal port. For example, the control information can beconfigured as shown in Table 7.

TABLE 7 Power boosting value RS port Muting value remarks 0 port 7 Usedas 0 dB 1 or 2 terminals data channel 1 port 8 Used as 0 dB 1 or 2terminals data channel 2 port 7 Used as RS 3 dB 3 or 4 terminals 3 port8 Used as RS 3 dB 3 or 4 terminals 4 port 9 Used as RS 3 dB 3 or 4terminals 5 port 10 Used as RS 3 dB 3 or 4 terminals

In Table 7, ‘value’ is the value transmitted as the control information,and ‘muting’ and ‘power boosting value’ are corresponding parameters.

Referring to FIG. 5 and FIG. 6, before the reference signals aretransmitted/received, the control information of the reference signalsis transmitted/received. According to the current G3PP LTE standard, thecontrol information for the reference signal port allocation isdelivered over the control channel (e.g., PDCCH), and one information isprovided for the allocated frame. Hence, in the subframe, the referencesignal port information is equally applied to every resource allocatedto the terminal. However, the subframe unit allocation scheme can causeresource inefficiency as shown in FIGS. 29A and 29B.

FIGS. 29A and 29B show an application example of subframe unit controlinformation in a wireless communication system according to anembodiment of the present invention. FIG. 29A illustrates that a basestation 110 communicates with seven terminals 120-1 through 120-7.Referring to FIG. 29A, the terminal 120-1 uses a port 7, the terminal120-2 uses a port 8, the terminal 120-3 uses a port 9, the terminal120-4 uses a port 10, the terminal 120-5 uses the port 7, the terminal120-6 uses the port 8, and the terminal 120-7 uses the port 9. In sodoing, as illustrated in FIG. 29B, the terminals 120-1 and 120-2 aremultiplexed in a subband#1 2950-1, the terminals 120-1 through 120-4 aremultiplexed in a subband#2 2950-2, the terminals 120-1 and 120-3 aremultiplexed in a subband#3 2950-3, the terminals 120-1 and 120-5 aremultiplexed in a subband#4 2950-4, the terminals 120-5 and 120-2 aremultiplexed in a subband#5 2950-5, and the terminals 120-5 and 120-7 aremultiplexed in a subband#6 2950-6. Referring to FIGS. 29A and 29B, asthe port information is applied to all of the subbands 2950-1 through2950-6, the two problems occur.

The first problem is that the port cannot move. For example, althoughthe subband #3 2950-3 does not use the port 8, the terminal 120-3 cannotuse the port 9 because the terminal 120-3 is using the port 9 in thesubband#2 2950-2. This is because the allocated port cannot bedesignated per subband. When the port 8 and the port 9 belong todifferent CDM groups, the first problem can additionally waste thereference signal resource. The second problem is that a terminalcombination not multiplexed occurs. For example, when MU-MIMO is to betransmitted to the terminal 120-1 and the terminal 120-5 through thesubband#4 2950-4, since both of the terminal 120-1 and the terminal120-5 use the port 7, the terminal 120-1 and the terminal 120-5 cannotbe MU paired.

Such problems are caused because the control information for thereference signals is not provided per subband. That is, when only onereference signal port information is transmitted for the whole resource,scheduling of the base station can be limited. Hence, the presentinvention provides various embodiments for the control informationconfiguration.

According to an embodiment of the control information configuration forthe reference signals, the control information is configured per subbandas shown in FIG. 30. FIG. 30 depicts a configuration of subband unitcontrol information in a wireless communication system according to anembodiment of the present invention. FIG. 30 shows control informationfor K-ary subbands.

Referring to FIG. 30, the control information includes a subband portindex. The control information can further include other parameter notdepicted in FIG. 30. That is, as shown in FIG. 30, the controlinformation includes the port indexes corresponding to the subbandsrespectively. Accordingly, the base station can allocate the ports toterminals in different combinations for each subband.

According to another embodiment of the control information configurationfor the reference signals, the control information is configured persubband group as shown in FIG. 31. FIG. 31 depicts a configuration ofresource group unit control information in a wireless communicationsystem according to an embodiment of the present invention. FIG. 31shows control information for K-ary subbands.

Referring to FIG. 31, K/2-ary resource groups 3160-1 through 3160-K/2are formed from K-ary subbands 3150-1 through 3150-K. The resource groupis an application unit of the control information for reference signals,and includes a plurality of subbands. In FIG. 31, one source groupincludes two subbands. However, according to various embodiments of thepresent invention, one resource group can include three or moresubbands. The resource group can be referred to as a resource blockgroup.

For doing so, resource group size information for reference signal portinformation transmission can be further added to resource group sizeinformation for legacy resource allocation. A specific value of theresource group size for the reference signals can be determined byconsidering trade-off between overhead of the control information andscheduling freedom of the base station.

The resource group size value can be predefined in the system, ortransmitted through a long duration RRC signal. The resource group sizefor the reference signals can be referred to as ‘I_(DM-RS)’.Specifically, the base station can transmit a parameter indicating theresource group size for the reference signal port through the RRCsignal. Hence, the terminal can determine the resource group size forthe reference signal port transmission by multiplying the resource groupsize used for general resource allocation by the parameter. For example,when the resource group size used for the general resource allocation isP and the parameter for the reference signal port is I_(DM-RS), theresource group size for the reference signal port transmission can bedetermined as P×I_(DM-RS). When the control information is configured asshown in FIG. 31, the base station can operate as shown in FIG. 32 andthe terminal can operate as shown in FIG. 33.

FIG. 32 depicts a reference signal transmitting procedure based oncontrol information notifying a resource group size in a wirelesscommunication system according to an embodiment of the presentinvention. FIG. 32 illustrates an operating method of the base station110.

Referring to FIG. 32, the base station transmits control informationindicating a resource group size corresponding to control information ofreference signals in step 3201. The resource group size indicates thenumber of subbands to which one control information is applied. Thecontrol information can be transmitted through an RRC message or as aDCI over a control channel of the subframe. Also, the controlinformation can include allocation information of the reference signals,for example, an antenna port, a CDM group, and the like. That is, thecontrol information includes a parameter indicating how many subbandsthe allocation information is applied to.

Next, the base station transmits reference signals in step 3203. In sodoing, the base station applies the same allocation information insubbands of the resource group size indicated by the controlinformation. That is, the base station can apply differentconfigurations (e.g., CDM group, antenna port) based on the subbands ofthe resource group size indicated by the control information.

FIG. 33 depicts a reference signal receiving procedure based on controlinformation notifying a resource group size in a wireless communicationsystem according to an embodiment of the present invention. FIG. 33illustrates an operating method of the terminal 120.

Referring to FIG. 33, the terminal receives control informationnotifying a resource group size corresponding to control information ofreference signals in step 3301. The resource group size indicates thenumber of subbands to which one control information is applied. Thecontrol information can be received through an RRC message or as a DCIover a control channel of the subframe. Also, the control informationcan include allocation information of the reference signals, forexample, an antenna port, a CDM group, and the like. That is, thecontrol information includes a parameter indicating how many subbandsthe allocation information is applied to.

Next, the terminal transmits reference signals in step 3303. In sodoing, the terminal applies the same allocation information in subbandsof the resource group size indicated by the control information. Thatis, the terminal can determine a resource unit for applying the sameparameter based on the resource group size, and detect at least onereference signal received in the resource unit based on the sameparameter. Specifically, the terminal can apply different configurations(e.g., CDM group, antenna port) based on the subbands of the resourcegroup size indicated by the control information.

According to another embodiment of the control information configurationfor the reference signals, the control information is divided accordingto an application range in FIGS. 34A and 34B. FIGS. 34A and 34B depict aconfiguration of control information divided based on an applicationrange in a wireless communication system according to an embodiment ofthe present invention.

Referring to FIG. 34A, a base station 110 communicates with terminals120-1 through 120-4. In so doing, the base station 110 transmits controlinformation for reference signals, that is, reference signalinformation. The control information can include a combination of SBinformation and WB information. The SB information includes a firstportion of control information applied on the subband unit, and the WBinformation includes a second portion of control information appliedbased on a plurality of subband units. For example, the WB informationcan designate the order in the CDM group, and the SB information candesignate the CDM group. For example, the control information can beconfigured as shown in Table 8.

TABLE 8 Port index WB information SB information 7 1 1 8 2 1 9 1 2 10 22

For example, referring to FIG. 34A, for the terminal 120-1, a first CDMgroup is allocated in a subband#1 3450-1, the first CDM group isallocated in a subband#2 3450-2, and the first CDM group is allocated ina subband#3 3450-3. Accordingly, the SB information for the terminal120-1 is set to “#1/#1/#1”. Also, with respect to the subbands 3450-1through 3450-3, since a port (e.g., a port 7) of the first order in thefirst CDM group is allocated to the terminal 120-1, the WB informationfor the terminal 120-1 is set to “#1”.

Also, referring to FIG. 34B, in case of the whole subband unit referencesignal port allocation depicted on the left side, since the terminal120-3 is allocated the port 9 in the subband#3 3450-3, the resource ofthe port 8 is wasted. However, according to an embodiment of the presentinvention depicted on the right side, the terminal 120-3 can use theport 10 or the port 8 per subband. That is, the reference signalresource can be used more effectively.

When the control information is configured as shown in FIGS. 34A and34B, the base station can operate as shown in FIG. 35 and the terminalcan operate as shown in FIG. 36.

FIG. 35 depicts a reference signal transmitting procedure based oncontrol information divided based on an application range in a wirelesscommunication system according to an embodiment of the presentinvention. FIG. 35 illustrates an operating method of the base station110.

Referring to FIG. 35, the base station transmits control informationwhich configures a first portion per subband and a second portion for aplurality of subbands in step 3501. That is, the first portion isapplied to each subband, and the second portion includes a parameterapplied to the subbands in common. For example, the second portion caninclude a parameter applied to the whole subband. The controlinformation can be transmitted through an RRC message or in the form ofDCI over a control channel of a subframe.

Next, the base station transmits reference signals in step 3503. In sodoing, the base station applies the parameters indicated by the firstportion and the second portion of the control information. In so doing,the base station applies at least one parameter of the second portion tothe subbands in common, and applies at least one parameter of the firstportion to each subband. For example, the first portion can designate aCDM group, and the second portion can designate the order in the CDMgroup.

FIG. 36 depicts a reference signal receiving procedure based on controlinformation divided based on an application range in a wirelesscommunication system according to an embodiment of the presentinvention. FIG. 36 illustrates an operating method of the terminal 120.

Referring to FIG. 36, the terminal receives control information whichconfigures a first portion per subband and a second portion for aplurality of subbands in step 3601. That is, the first portion isapplied to each subband, and the second portion includes a parameterapplied to the subbands in common. For example, the second portion caninclude a parameter applied to the whole subband. The controlinformation can be received through an RRC message or in the form of DCIover a control channel of a subframe.

Next, the terminal receives reference signals in step 3603. In so doing,the terminal applies the parameters indicated by the first portion andthe second portion of the control information. In so doing, the terminalapplies at least one parameter of the second portion to the subbands incommon, and applies at least one parameter of the first portion to eachsubband. That is, the terminal determines the parameter per subband bycombining the first portion and the second portion, and detects thereference signals based on the parameter per subband.

For example, the first portion can designate a CDM group, and the secondportion can designate the order in the CDM group.

According to yet another embodiment of the present invention for thecontrol information configuration for the reference signals, the controlinformation only for all of the subbands and the control informationaccording to an embodiment of the present invention can be selectivelyused. Herein, the control information according to an embodiment of thepresent invention includes one of the control information per subband,the control information per resource group, and the control informationdivided to the WB information and the SB information. For example, thesystem can define the port information of the two types in different DCIformats, and the terminal can interpret the two DCI formats respectivelyand thus concurrently perform the detection. The terminal can determinethe DCI format of the successful detection as the reference signal portinformation transmitted by the base station. In this case, the basestation can determine whether to configure the reference signal portinformation for all of the subbands or per subband based on a pairingsituation of the MU-MIMO terminals and a control level aggregation levelper terminal.

The methods according to embodiments described in the claims or thespecification of the present invention can be implemented in hardware,software, or a combination of hardware and software.

As for the software implementation, a computer-readable storage mediumstoring one or more programs (software modules) can be provided. One ormore programs stored in the computer-readable storage medium can beconfigured for execution by one or more processors of an electronicdevice. One or more programs can include instructions for enabling theelectronic device to execute the methods according to the embodimentsdescribed in the claims or the specification of the present invention.

Such a program (software module, software) can be stored to a randomaccess memory, a non-volatile memory including a flash memory, a ReadOnly Memory (ROM), an Electrically Erasable Programmable Read OnlyMemory (EEPROM), a magnetic disc storage device, a compact Disc(CD)-ROM, Digital Versatile Discs (DVDs) or other optical storagedevices, and a magnetic cassette. Alternatively, the program can bestored to a memory combining part or all of those recording media. Also,a plurality of memories may be included.

Also, the program can be stored in an attachable storage deviceaccessible via a communication network such as Internet, Intranet, LocalArea Network (LAN), Wide LAN (WLAN), or Storage Area Network (SAN), or acommunication network by combining these networks. Such a storage devicecan access the device which carries out an embodiment of the presentinvention through an external port. Also, a separate storage device onthe communication network may access the device of the presentinvention.

In the specific embodiments of the present invention, the elementsincluded in the invention are expressed in a singular or plural form.However, the singular or plural expression is appropriately selectedaccording to a proposed situation for the convenience of explanation,and the present invention is not limited to a single element or aplurality of elements. The elements expressed in the plural form may beconfigured as a single element and the elements expressed in thesingular form may be configured as a plurality of elements.

While the specific embodiment has been described in the specification ofthe present invention, it will be understood that various changes can bemade therein without departing from the scope of the present. Therefore,the scope of the invention is not limited to the described embodimentsbut is defined by the scope of the claims to be explained and theirequivalents.

1. A method for operating a terminal in a wireless communication system,the method comprising: receiving information for reference signals froma base station; and receiving the reference signals according to theinformation, wherein the information comprises information indicating alength of an orthogonal code applied to the reference signals. 2.(canceled)
 3. The method of claim 1, wherein the information indicatesat least one port allocated to the terminal, and wherein the at leastone port comprises at least one of a port 7, a port 8, a port 11, or aport
 13. 4. The method of claim 1, wherein, if a port 7 or a port 8 isallocated to the terminal, the information indicates the length of theorthogonal code with a first length value or a second length value, andwherein, if a port 11 or a port 13 is allocated to the terminal, theinformation indicates the length of the orthogonal code with the secondlength value.
 5. The method of claim 4, wherein the first length valueis 2, and wherein the second length value is
 4. 6. The method of claim1, wherein the information comprises a single value indicating acombination of the length of the orthogonal code, at least one antennaport allocated to the terminal, and a number of layers allocated to theterminal.
 7. The method of claim 1, wherein the length of the orthogonalcode is determined based on a number of multiplexed terminals.
 8. Themethod of claim 1, wherein the terminal is capable of interpretingorthogonal codes of a first length and orthogonal codes of a secondlength that is greater than the first length, and, when the terminal ismultiplexed with another terminal incapable of interpreting orthogonalcodes of the second length, an orthogonal code allocated to the terminalhas orthogonality with an orthogonal code allocated to the anotherterminal within a range of the first length.
 9. The method of claim 1,wherein the reference signals are precoded identically with data signalstransmitted to the terminal.
 10. The method of claim 1, wherein thereference signals are transmitted on a same resource as referencesignals for another terminal spatially multiplexed, and the referencesignals and the reference signals for the other terminal are separableby the orthogonal code.
 11. The method of claim 1, wherein theinformation comprises first portion information applied to a pluralityof subbands in common and second portion information applied persubband.
 12. (canceled)
 13. The method of claim 1, wherein theinformation comprises information indicating a power boosting valueapplied to the reference signals.
 14. The method of claim 1, wherein theinformation comprises information indicating whether reference signalsfor another multiplexing group are transmitted.
 15. (canceled)
 16. Aterminal in a wireless communication system, the terminal comprising: atransceiver configured to: receive information for reference signalsfrom a base station; and receive the reference signals according to theinformation, wherein the information comprises information indicating alength of an orthogonal code applied to the reference signals.
 17. Theterminal of claim 16, wherein the information indicates at least oneport allocated to the terminal, and wherein the at least one portcomprises at least one of a port 7, a port 8, a port 11, or a port 13.18. The terminal of claim 16, wherein, if a port 7 or a port 8 isallocated to the terminal, the information indicates the length of theorthogonal code with a first length value or a second length value, andwherein, if a port 11 or a port 13 is allocated to the terminal, theinformation indicates the length of the orthogonal code with the secondlength value.
 19. The terminal of claim 18, wherein the first lengthvalue is 2, and wherein the second length value is
 4. 20. The terminalof claim 16, wherein the information comprises a single value indicatinga combination of the length of the orthogonal code, at least one antennaport allocated to the terminal, and a number of layers allocated to theterminal.
 21. A base station in a wireless communication system, thebase station comprising: a transceiver configured to: transmitinformation for reference signals to a terminal; and transmit thereference signals to the terminal according to the information, whereinthe information comprises information indicating a length of anorthogonal code applied to the reference signals.
 22. The base stationof claim 21, wherein the information indicates at least one portallocated to the terminal, and wherein the at least one port comprisesat least one of a port 7, a port 8, a port 11, or a port
 13. 23. Thebase station of claim 21, wherein, if a port 7 or a port 8 is allocatedto the terminal, the information indicates the length of the orthogonalcode with a first length value or a second length value, and wherein, ifa port 11 or a port 13 is allocated to the terminal, the informationindicates the length of the orthogonal code with the second lengthvalue.